1991 carbs on a 1980 engine

[btfulmer]

Okey I was asked to post some pics of the 34mm carb mod I did on my Bobber. Things to aquire; one set of carbs from a 1990 or later CB750, one set of intake clamps, 4 each 30 degree silicon tubes, and some card board.

Make a templet of the carbs intake runner side with the card board, (this needs to be done because the 90 and latter model carbs are a touch closer together than the 30MM ones)

Then it is just a matter of cutting tue tubes for the proper angles to go from the head to the carb templet. (a minor note here is the both sides of the tubes will need to be cut to acheave proper angle)

The throdle cable should line up with minor adjustments, the pull close side just gets crimped around the cable housing to keep it in place ( I'm working on making a new bracket for it)

Jet the carbs as needed depending on the needs of the engine and enviroment you live in.

 

[MK3Brent]

Very cool, man.

 

[btfulmer]

These carbs will crank this motor from idle to 9k in a heart beat, and cruz 65mph at 4k in 5th gear. No idle problems, no flat spots, no hesitation.
They really make the DOHC motors run good. One thing to note is the exhaust is a 4 into 2 with flow through 2" baffels.

 

[K2750tracy]

I really like the hard line set up on your fuel petcock too. Very neat and clean.

 

[Field]

Do you ever look inside your crankcase filters for any white goo? (condensation and oil)

That is one thing the stock one did nice, was goo would form up near the three way split. I wonder how the form you have works.

 

[Hans18]

Btfulmer, I ordered some 91 nighthawk carbs for my 79 cb750k. The spacing is off quite a bit as you described.

How is your setup holding up? I'm trying to decide on making them work or going with something else

Thanks

 

[amc49]

I have trouble understanding why one goes to all this work when the OEM carbs work fine and all day long. Haven't really done anything as the carbs are still CV type and they do NOT open all the way even if your right hand says to. And now you have to worry about rubber diaphragm issues whereas the OEM ones had no diaphragms.

The stock OEM carbs run to 10 grand easy as spit if the motor is in good condition, which is the mistake that most change carbs trying to fix. Engine off in ring or valve seal will NOT open CV carbs up and doesn't matter what kind you have. As well, bigger carbs are not bigger if CVs, the engine will only open the slides part way on the bigger ones, what ALL CVs do when you get them too big. Why Japan uses them and why you all are so impressed by the later 'bigger' carbs, it's an American testosterone bragging rights thing that really doesn't impact spit.

 

[Hans18]

I appreciate your feedback. This is my first build, I just bought a project bike a week ago. The bike was a rolling frame, brand new wIting harness, and engine with good compression (cold tested 140 psi across the board). It lacks carbs, exhaust etc etc, needs a lot of rework but not enough to where I felt I was in way over my head.

I'm not looking at carbs as a performance mod, or testosterone bragging rights as you referred to, just looking for something to function, and possibly something a little easier for me to work on, rather than getting myself into an oem carb rebuild. Instead, I was able to find a really nice set from a nighthawk for a really good price. Price is everything to me at the moment since I'm fresh out of college a year ago working my first job.

I was posting on this thread for feedback on how these carbs are holding up.

Thanks

 

[amc49]

Your call and do what you will. Not having carbs could make a difference.

However, this.............

'...possibly something a little easier for me to work on, rather than getting myself into an oem carb rebuild.'

Says scads. You are biting off a carb set nowhere near dialed in for optimum use like an OEM set is. People think you can jump them from application to application and being CV that is easier but by no means done. If you end up spending all you saved getting them to run right, well, what's with that? It happens all the time. The owners then think they run great commonly until they get to drive one running right then they are not so happy. I've seen it so many times I cannot count. Each carb bank is matched to that one engine and not just the mainjets, rather every single part inside, that can be a bunch. Note the last sentence in the OP there, he is trying to tell you.

Yeah, I know, the owner says this or that. I used to fix stuff from owners that swore that all day long and a big part of the problem. The owner has to be fixed before you can even think about fixing the machine. BTDT a thousand times.

They may work, but if they don't like stated, you now know why. Some day I'll tell the story of my next door neighbor who had a Kawasaki 750 three and always bragging about how great it ran...........perfectly. Until I fixed it one day for him after getting sick of hearing a three cylinder machine that ran on only two cylinders. I wasn't thinking that one out fully, I could have killed that guy................